The disclosed invention is directed generally to hybrid multilayer circuit structures, and is directed more particularly to hybrid multilayer circuit structures having capacitors formed in the vias thereof.
Hybrid multilayer circuit structures, also known as hybrid microcircuits, implement the interconnection and packaging of discrete circuit devices, and generally include a unitized multilayer circuit structure formed from a plurality of integrally fused insulating layers (e.g., ceramic layers) having conductor traces disposed therebetween. The discrete circuit devices (e.g., integrated circuits) are commonly mounted on the top insulating layer so as not to be covered by another insulating layer or on an insulating layer having die cutouts formed thereon to provide cavities for the discrete devices. Passive components such as capacitors and resistors can be formed on the same layer that supports the discrete devices, for example, by thick film processes, or they can be formed between the insulating layers, for example, also by thick film processes. Electrical interconnection of the conductors and components on the different layers is achieved with vias or holes appropriately located and formed in the insulating layers and filled with conductive material, whereby the conductive material is in contact with predetermined conductive traces between the layers that extend over or under the vias.
The traditional thick film processes for making capacitors involves screen printing a first capacitor plate on one of the dielectric layers, forming a capacitor dielectric layer over the first capacitor plate, and then forming a second capacitor plate over the dielectric layer. For example, the capacitor dielectric layer is formed by screen printing on the first capacitor plate, and the second capacitor plate is formed by screen printing on the capacitor dielectric or on the bottom side of the dielectric layer that overlies the layer on which the first capacitor plate is formed.
A consideration with screen printed capacitors is the difficulty in controlling their values, and the requirement for precision capacitors is met by mounting discrete capacitors on the top dielectric layer along with other discrete devices, and/or by forming screen printed capacitors on the top layer which are trimmed, for example, by laser or abrasive trimming. The requirement for precision capacitors has also been met by formation and trimming of buried screen printed capacitors, as disclosed in commonly assigned U.S. Pat. No. 4,792,779.
A further consideration with screen printed capacitors as well as discrete capacitors is the substrate area utilized by such components.